Re: [PATCH] qdisc oops fix

[jamal]

On Wed, 16 Apr 2003, Manfred Spraul wrote:

> jamal wrote:
>
> >This is a different problem from previous one posted.
> >
> >Theres a small window (exposed given that you are provisioning a lot
> >of qdiscs  and running traffic at the same time) that an incoming packet
> >interupt will cause the BUG().
> >
> >GFP_ATOMIC will fix it, but i wonder if it appropriate.
> >
> >
> This is a 2.4 kernel, correct?
>

Catalin, Can you what kernel that is?

> >>With many rules (~5000 classes and ~3500 qdiscs and ~50000 filters)
> >>the kernel oopses in slab.c:1128.
> >>
> This check?
>        if (in_interrupt() && (flags & SLAB_LEVEL_MASK) != SLAB_ATOMIC)
>                 BUG();

thats the one i meant.

> It's triggered, because someone does something like
>     spin_lock_bh(&my_lock);
>     p = kmalloc(,GFP_KERNEL);
>
> I don't like the proposed fix: usually code that calls
> kmalloc(,GFP_KERNEL) assumes that it runs at process space, e.g. uses
> semaphores, or non-bh spinlocks, etc.
> slab just happens to contain a test that complains about illegal calls.

ok. Nice.

>
> >>Trace; c0127e0f <kmalloc+eb/110>
> >>Trace; c01d3cac <qdisc_create_dflt+20/bc>
> >>Trace; d081ecc7 <END_OF_CODE+1054ff0f/????>
> >>Trace; c01d5265 <tc_ctl_tclass+1cd/214>
> >>Trace; d0820600 <END_OF_CODE+10551848/????>
> >>Trace; c01d27e4 <rtnetlink_rcv+298/3bc>
> >>Trace; c01d0605 <__neigh_event_send+89/1b4>
> >>Trace; c01d7cd4 <netlink_data_ready+1c/60>
> >>Trace; c01d7730 <netlink_unicast+230/278>
> >>Trace; c01d7b73 <netlink_sendmsg+1fb/20c>
> >>Trace; c01c79d5 <sock_sendmsg+69/88>
> >>Trace; c01c8b48 <sys_sendmsg+18c/1e8>
> >>Trace; c0120010 <map_user_kiobuf+8/f8>
> >>
> >>
> >>
> >>
> I don't understand the backtrace. Were any modules loaded? Perhaps
> 0xd081ecc7 is a module.
>

Probably a module. Again Catalin, run no modules.

> I'd add a
>     if(in_interrupt()) show_stack(NULL);
> into qdisc_create_dflt(), and try to reproduce the bug without modules.
>

Catalin - again instead of your fix can you please add this call?

cheers,
jamal